1. Field of the Invention
The present invention generally relates to a recording apparatus related to an ink jet recording apparatus using an elongate head having an array of a number of nozzles extending over a relatively long range, or what is called a full multi-head (also called as a full line head) having an array of a number of nozzles extending over a range corresponding to a length along a width of recording paper, a recording method thereof, and a program. More specifically, the present invention relates an ink jet recording apparatus using, as the full multi-head, an elongate print head, or what is called a joint head, in which a plurality of relatively short chips, each having a plurality of nozzles, are arranged so as to be accurately joined together, a recording method thereof, and a program.
2. Description of the Related Art
Various types of recording apparatuses are available. Some of them are used for printers, copying machines, and the like. Others may be used as output devices for multifunctional equipment including computers and word processors, and for workstations. Each of these different types of recording apparatuses is designed to print an image (including characters and symbols) on a recording medium that may be paper, a thin sheet of plastic, or the like, based on print information. Such recording apparatuses may be classified into an ink jet type, a wire dot type, a thermal type, a laser beam type, and the like according to a printing method employed.
A serial type recording apparatus is known. The serial type apparatus performs a print action through a scanning motion in a direction (a main scanning direction) perpendicular to a direction (a sub scanning direction) of transport of a recording medium. In such a recording apparatus, print means (a print head) traveling along the recording medium forms the image. Each time a print action for one scanning motion is completed, the recording apparatus transports the recording medium a predetermined amount. The recording apparatus then performs a new print action in the subsequent scanning motion for the recording medium that has thereafter been brought to another stop. By repeating a sequence of these actions, the recording apparatus produces a printed output for the entire area of the recording medium.
Another type of the recording apparatus, a line printer (also called as a full line type) is available. A print action involved with the line printer is a motion in the sub scanning direction, or the direction of transport of the recording medium. Such a type of recording apparatus produces a printed output for the entire area of the recording medium as follows. Specifically, the recording medium is loaded at a prescribed position and, while a print action for each entire line of the image is carried out continuously, the recording medium is transported a predetermined amount.
Of the various types of recording apparatuses described in the foregoing, the ink jet type recording apparatus (the ink jet recording apparatus) carries out a print action by expelling ink from print means or the print head relative to the recording medium. The ink jet recording apparatus offers a number of benefits as detailed in the following. Specifically, it is easy to build the print head compact; an image of high resolution can be formed at high speed; a running cost is low, since the method requires no special treatment on plain paper; noise is low because the action is a non-impact type; it is easy to configure a structure for forming a color image by using ink of different colors; and the like.
One known type of the ink jet recording apparatus attracts attention as a printer for on-demand printing, of which there is lately a growing need. Specifically, this type of ink jet recording apparatus is of line printer configuration. The apparatus uses what is called the full multi-type print head formed by an array of a number of ink jet recording elements (nozzles, ink ejection ports) arranged in a direction perpendicular to the direction of transport of the recording medium. The apparatus permits image formation performed at even higher speed.
A print speed on the order of 100,000 printed pages per hour, as in printing of conventional newspapers and magazines in units of several million copies, is not required of on-demand printing. Rather, labor saving is at a premium in on-demand printing. Though inferior in print speed to conventional offset printing machines or the like, the full multi-head line printer eliminates the need for making printing plates. Because of this labor saving feature, the full multi-head line printer is just right for on-demand printing.
A capability of producing 30 or more printed pages of A3 recording medium with a specific resolution of 600×600 dpi (dots/inch) for text and mono-color originals and of 1200×1200 dpi or higher for full-color originals, such as photos, is required of the full multi-head line printer used for the on-demand printing. Needs also exist, on the other hand, for producing an output of an image shot by a digital camera or the like on a conventional L-format size and on a small-sized medium, such as a postcard or the like. The full multi-head line printer may therefore be said to be used in a number of cases, in which printing involves recording media of several different sizes.
A major problem with the full multi-head printer was, however, difficulty involved in machining with no defects the entire ink jet recording elements (nozzles) provided over an entire width of a print area. For a full multi-head printer producing a printed output of a photo grade on large-sized paper, including reference materials produced for office use, for example, it is required that the printer be capable of producing the output onto recording paper of A3 size. This requires a full multi-head having a recording width of about 280 mm. To print on A3 size paper at 1200 dpi, therefore, it becomes necessary to provide about 14,000 nozzles for a single full multi-head for recording the image of one color. Because of manufacturing processes involved, it is extremely difficult to machine the entire ink jet recording elements corresponding to this large number of nozzles with no defects allowed whatsoever. Should it be possible to machine the elements properly, a conformance rate must be very low with an exorbitant amount of cost involved in manufacturing.
A known ink jet recording apparatus of the line printer configuration using the full multi-head therefore employs what is called a joint head to achieve the intended purpose. The joint head specifically refers to a print head that is an array of a plurality of relatively inexpensive, short-length chips (a group of nozzles) used in the serial type arranged accurately to make an elongate print head.
Benefits of using the joint head include: a reduced manufacturing cost thanks to an improved manufacturing yield rate; the maximum print width of the print head can be changed relatively easily according to the number of short-length chips placed.
There is, however, a problem about the joint head, in which an image quality at a joint between chips tends to be degraded because of a structure of the joint head involved. Specifically, deviation produced in the arrangement of the chips causes a nozzle pitch between adjacent nozzles at the joint to change relative to a nozzle pitch between adjacent nozzles at portions other than the joint. This results, in many cases, in a joint line occurring at a portion of the image produced corresponding to the joint.
As noted earlier, the joint head is an array of a plurality of short-length chips, each having an arbitrary number of nozzles. It is therefore easy to configure print heads of varying print widths by simply changing the number of chips placed. On the other hand, it is difficult to construct a print head having a width equivalent to the print width required for printing of the recording medium (ordinary standard sizes). A common approach is therefore to construct a print head such that the width of the print head is wider than the maximum width of the recording medium. This is accomplished by increasing the number of chips placed. This, in turn, means that there is a group of nozzles that are not to be used.
Various solutions have so far been proposed to these problems relating to the joint head. First, the following approaches are proposed for the solutions to the joint line. The approaches are intended for enhancing physical machining accuracy of the head: specifically, for example, a method of accurately arranging chips at the joint with a high chip arrangement accuracy; and an arrangement apparatus used to minimize deviation in nozzle pitch.
Another proposed method is to arrange chips such that several nozzles at ends of different chips overlap each other, instead of placing an end nozzle of one chip adjacent to an end nozzle of another chip at the joint. According to this method, ink is ejected from the two mutually overlapping nozzles during printing. The image is thereby processed so as to make the joint line less noticeable. Still another proposed method is to vary the amount of ink drops ejected from the nozzles of the joint of the chips, thereby making the joint less noticeable.
A solution is proposed to the problem of disposition of groups of non-use nozzles arising from a difference between the recordable width of the print head and the maximum width of the recording medium. This difference in width is produced due to two or more chips arranged, each having an arbitrary number of nozzles. The proposed solution is to configure the non-use nozzles as ejection-disabled nozzles by leaving them disconnected from a circuit concerned. A further approach is proposed to use part of the ejection-disabled nozzles as ejection-enabled ones in terms also of circuit configuration, if heads are disposed in the printer so that the chip joint is varied for each color. This approach is to prevent the image from being degraded by the joint.
A number of patent documents disclose techniques relating to the joint head as described heretofore. Examples of such patent documents include Japanese Patent No. 2980429, Japanese Patent Application Laid-Open No. 6-255098(1994), Japanese Patent Application Laid-Open No. 11-198380(1999), Japanese Patent Application Laid-Open No. 2001-001510, and Japanese Patent Application Laid-Open No. 2001-199074.
It is, however, considered that the solutions proposed in these patent documents are not effective enough to solve the problem of degraded image quality at the chip joints throughout the entire image area, in printing the image on recording media of varying sizes using the joint head. The conventional techniques are yet to be improved in that uneven streaks and moiré that are particularly noticeable in ends of the image tend to occur if the ends of the image are included in the chip joint. The problematic symptoms are particularly noticeable when printing is made through overlapping of chip joints.